Photoconductor containing printing plates

ABSTRACT

A planographic printing plate is prepared by exposing imagewise a copy medium comprising a physically developable photosensitive material such as a photoconductor and contacting the copy medium with image-forming materials which remain chemically reactive in the non-exposed areas of the copy medium but become substantially chemically non-reactive in the exposed areas, and contacting the thus treated copy medium with a compound having an oleophilic grouping and a grouping reactive with the chemically reactive image-forming materials of the non-exposed areas of the copy medium, thereby producing a positive oleophilic image of the original. The image-forming materials and/or oleophilic compound having a reactive grouping may be incorporated in the copy medium prior, during, or subsequent to exposure. This printing plate containing the oleophilic image is suitable for contacting with ink to produce multiple copies. When a greasy printing ink is used a positive of the original (positive to positive) is produced.

United States, Patent [1 1 Gracia 451 Feb. 19, 1974 PHOTOCONDUCTORCONTAINING PRINTING PLATES [75] Inventor: Robert F. Gracia, Scituate,Mass. [73] Assignee: Itek Corporation, Lexington, Mass.

[22] Filed: NOV. 8, 1971 21 Appl. No.: 196,445

Related US. Application Data [63] Continuation-impart of Ser. No.743,738, July 10,

1968, abandoned.

[52] US. Cl. 96/33, 96/48 PD, 101/456,

. 101/458 [51] Int. Cl. G03f 7/02, G030 5/24 [58] Field of Search..-..96/33, 48 PD; 101/456, 458, 101/466 [56] References Cited UNITED STATESPATENTS 3,083,097 3/1963 Lassig eta]. 96/33 3,161,508 12/1964 Hepher etal. 96/33 3,490,906 l/l970 Blake 96/33 FOREIGN PATENTS OR APPLICATIONS1,043,250 9/1966 Great Britain 9 6/27 R Primary Examiner-David KleinAttorney, Agent, or Firm-Homer 0. Blair; Robert L. Nathans; W. GaryGoodson s71 ABSTRACT A planographic printing plate is prepared byexposing imagewise a copy medium comprising a physically developablephotosensitive material such as a photoconductor and contacting the copymedium with imageforming materials which remain chemically reactive inthe non-exposed areas of the copy medium but become substantiallychemically non-reactive in the exposed areas, and contacting the thustreated copy medium with a compound having an oleophilic grouping and agrouping reactive with the chemically reactive image-forming materialsof the non-exposed areas of the copy medium, thereby producing apositive oleophilic image of the original. The image-forming materialsand/or oleophilic compound having a reactive grouping may beincorporated in the copy medium prior, during, or subsequent toexposure. This printing plate containing the oleophilic image issuitable for contacting with ink to produce multiple copies. When agreasy printing ink is used a positive of the original (positive topositive) is produced.

10 Claims, 3 Drawing Figures PAIENTEOFEBI w 3,793.024

EXPOSURE DEVELOPED NEGATIVE PRINTING PLATE ROBE/i 7' F. 6R4 6/4INVENTOR.

ATTORNEY.

BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinventionrelates to processes for the production of photographic imagesespecially useful as printing plates and to products obtained thereby.

2. Description of the Prior Art Data or image storage media comprisinga-p'hotoconductor such as TiO are described in detail in U.S.?Pat. Nos.3,152,903; 3,052,541; 3,380,823; and British Pat. specification No.1,043,250. In the aforementioned British patent specification, aradiation sensitive material, such as TiO functions as aphotosensitivecomponent of the media and exposure of these media to activatingradiation results in the storage of reversible latent images therein.The reversible latent image pattern may be converted to an irreversibleform by contacting with suitable image-forming materials prior to,during, or subsequent to exposure.

SUMMARY OF THE INVENTION It has been discovered according to thisinvention that a planographic printing plate suitable for producingmultiple copies of an original maybe produced by contacting a copymedium comprising a physically developable material such as aphotoconductor which has been imagewise exposed and contacted withchemically reactive image-forming materials and with a coma metallicimage and in the non-metallic areas a solution of metal ions, iscontacted with an oleophilic compound of the type described herein toform a reaction product between the metal ions and the oleophiliccompound which is more oleophilic than any intereaction of theoleophilic compound with the metallic image. Therefore, when the copymedium thus formed is used as aprinting plate, greasy ink will adherepreferentially to those areas "which originally contained the metal ionrather than those areas containing the metallic image areas. Thus, themetallic image containing area "becomes a non-printing area indistinction from the prior art wherein the metallic image becomes a"printing image when contacted with these same oleoiphilic compounds andwhen used with a greasy printing ink.

pound having an oleophilic grouping and a grouping reactive with thechemically reactive image-forming materials remaining in the non-exposedareas of the copy medium and non-reactive with the images in the exposedareas of the copy medium, thereby "producing a positive oleophilicimageof the original image. Some or all of the image forming materialsand oleophilic compound having a reactive grouping may be applied to thecopy medium prior to exposure. The planographic printing plate ispreferably produced by first imagewise exposing the copy medium and thencontacting the exposed copy medium with a physical developer preferablycomprising separatesolutions of a solution of metal ions and a solutionof a reducing agent for the metal ions, and then contacting the thusdeveloped copy medium with a heterocyclic mercaptan compound or the saltof such compound. If desired this invention may be practicednon-photographically by typing or writing on a support 'to form an imagepattern of chemically reactive image'forming materials. Thus, a

solvent permeable support may be written on with a so-' tiveimage-forming materials and the oleophilic compound produces a moreoleophilic area than the reaction product, if any, of areas which do notcontain these chemically reactive image-forming materials. Thus, in thepreferred embodiment 'a copy medium comprising DRAWINGS FIG. 1 is adiagrammatic view of the exposure step of one embodiment of thisinvention.

FIG. 2 is a diagrammatic view of the exposed photosensitive copy mediumof FIG. 1 which has been developed.

- FIG. 3 is a diagrammatic view of the developed copy medium of FIG. 2which has been made ink receptive in the non-image areas.

In general FIG. 1 describes the exposure of a photosensitive copy mediumcomprising a support 11 and a photosensitive coating 12 which ispreferably a photoconductor or other physically developablephotosensitive material through a transparency 20.

Physical development of the exposed copy medium of FIG. 1 produces adeveloped negative of the original transparency having metal images 13and non-image 14 having metal ions which are chemically reactive.

FIG. 3 shows a printing plate having oleophilic areas which correspondto the darkened portions of the original transparency 20. The printingplate of FIG. 3 can then "be inked and used as a printing plate forproducing multiple copies.

DESCRIPTION OF PREFERRED EMBODIMENT( S) The compounds having anoleophilic grouping and a grouping reactive with thechemically-reactiveimageforming materials of the non-exposed areas of the copy mediumsometimes referred to as the oleophilic compound of this invention) arepreferably polar solvent soluble organic compounds such as the polarsolvent soluble salts "of compounds disclosed in U.S. Pat. No.3,083,097, incorporated herein by reference. The preferred compounds aremetal salts which are soluble in a polar solvent and which will readilyundergo a metathetica] reaction with a solution of metal ions. Ametathetical reaction is defined herein as a chemical reaction whereinan exchange of ions takes place. For example, a solution of a sodiummercaptide will react with a solution of silver nitrate to form sodiumnitrate and a silver mercaptide. The sodium and potassium salts of theoleophilic compounds of this invention are especially preferred. Thepreferred oleophilic compound of this invention is the polar solventsoluble metal salts of RX wherein X is at least one reactive groupingcapable of reacting with the chemicallyreactive' image-forming materialsof the non-exposed areas of a copy medium which have been exposed andcontacted with image-forming materials, according to 3 the teachings ofthis invention. X preferably includes the following groups:

2. SR where R is a group which can easily be hydrolyzed leaving -SH,such as acoyl, aroyl, amidinium or NHR wherein R is alkyl, aryl,aralkyl, cycloalkyl, heterocyclyl,

3. Thio-acid groups,

4. Thio-amide groups,

5. Thione groups,

6. Selenium analogues of the foregoing groups (I),

( and 7. Isothiocyanate group.

R is at least one oleophilic group. The oleophilic group may be a fattychain or substituent containing at least four carbon atoms andpreferably 6-20 carbon atoms. R can also be an aryl, alkaryl, or aralkylgroup. The oleophilic grouping R is preferably a hetero grouping of thefollowing general formula:

wherein R represents aryl (phenyl, tolyl), aralkyl (benzyl), cycloalkyl(cyclohexyl), alkyl, preferably a long-chained straight or branchedchain, saturated or unsaturated hydrocarbon radical with at least 10,preferably 10 to carbon atoms, and a heterocyclic radical (furfuryl,thiazolyl), which substituents are either linked to one of the two Aatoms, and A represents one or more of the hetero atoms 0, N, S, and Se,which are present either in'an open arrangement or as ring elements of aheterocyclic ring, such as for example, l,3,4-triazole,1,3,4-thiodiazole, thiazole, selenazole or oxazole, and Rrepresentsaryl, aralkyl, cycloalkyl, alkyl, and a heterocyclic radicalwhich substituents are either linked to one of the two A groups directlyor by means of other linking groups, or linked to one of the ringelements of the heterocyclic ring.

The alkali and alkaline earth metal salts of the compounds having theformula R X are particularly useful in this invention.

Compounds especially preferred for this invention are the alkali andalkaline earth metal salts of the following heterocyclic mercaptans:

5-mercapto-3-phenyll ,3 ,4-thiadiazole-2-thione 2-mercaptobenzimidazole10 .......A.......A.. H W V l 2-mercaptobenzothiazole Compounds of thisclass can be prepared by the method of or analogous to the methoddescribed by Burke, J.A.C.S., 69, 236-7 (1947).

A simple test to determine whether a preferred class of oleophiliccompounds is suitable for this invention is to contact this compoundwith an aqueous solution of 0.01 N AgNO If a cloudy precipitate formsthe oleophilic compound is suitable for use.

Polar solvent suitable for dissolving the oleophilic compound of thisinvention are materials which will allow ionization of this oleophiliccompound and reaction with the chemically reactive image-formingmaterials of this invention. Water and simple alcohols are especiallypreferred.

The physically developable photosensitive material useful in thisinvention is preferably a photoconductor or photocatalyst and is notlimited to any group of compounds but may include bothorganic andinorganic photosensitive materials. Preferred photoconductors useful inthis invention are metal containing photoconductors. A preferred groupof such photosensitive materials are the inorganic materials such assilver halide and compounds of a metal and a non-metallic element ofgroup VIA of the periodic table*(*Periodic table from Langes HANDBOOK OFCHEMISTRY, 9th Edition, pp. 56-57, 1956.) such as metal oxides, such aszinc oxide, titanium dioxide, zirconium dioxide, germanium dioxide,indium trioxide, tin oxide, and barium titanate; metal sulfides such ascadmium sulfide, zinc sulfide and tin disulfide; metal selenides such ascadmium selenide. Metal oxides are especially preferred photoconductorsof this group. Titanium dioxide is a preferred metal oxide because ofits unexpectedly good results. Titanium dioxide having an averageparticle size less than about 250 millimicrons and'which has been heattreated in an oxidizing or a reducing atmosphere is especiallypreferred.

Organic photoconductors suitable for use in this invention are, forexample, the heteropolyacids such as phosphotungstic acid,phosphosilicic acid, and phosphomolyidic acid.

When a reversibly activatable photoconductor such as titanium dioxide isused, it should be conditioned before exposure by such methods asheating or storage in the dark from one to twenty-four hours. Afterconditioning, the photoconductor is not exposed to light prior to itsexposure to activating radiation for recording an image pattern.

Physically developable materials such as the vdiazosulphonates and likematerials disclosed in US. Pat. No. 2,738,272, incorporated herein byreference are also useful in this invention.

While the exact mechanism of the present process is 'not known it isbelieved that the presensitization, i.e.,

exposure to activating light, e.g., ultraviolet light,

cordingly, a simple test to determine whether materials have aphotoconductor effect is to mix the material in question with aqueoussilver nitrate. In the absence of light, little, if any, reduction ofsilver ions should occur. At the same time as exposing the same mixtureto light, a control sample of an aqueous silver nitrate solution aloneis similarly exposed and if the mixture darkens faster than the controlsample, the test material is a ,photoconductor.

The period of exposure will depend upon the intensity of the lightsource, particular photoconductor, the type and amount of catalyst, ifany, and like factors known to the art. In general, however, theexposure may vary from about 0.001 seconds to several minutes.

Image-forming materials which are useful in this invention are thosesuch as described in U.S. Pat. Nos. 2,738,272 and 3,152,903 and inBritish Pat. specification No. 1,043,250. These image-forming materialsinclude preferably an oxidizing agent and a reducing agent. Suchimage-forming materials are often referred to in the art as physicaldevelopers. The oxidizing agent is generally the image-forming componentof the image-forming material. However, this is not necessarily true.Either organic or inorganic oxidizing agents may be employed as theoxidizing component of the imageforming material. Preferred oxidizingagents comprise the reducible metal ions having at least the oxidizingpower of cupric ion and include such metal ions as Ag", n +a p 2 +z s +2+2 Cu, and Cu".

The reducing agent component of the image-forming materials of thisinvention are inorganic compounds such as the oxalates, formates, andethylenediaminetetraacetate complexes of metals having variable valence;and organic compounds such as dihydroxybenzenes, aminophenols, andaminoanilines. Also, polyvinylpyrrolidone, hydrazine, and ascorbic acidmay be used as reducing agents in this invention. Suitable specificreducing compounds include hydroquinone or derivatives thereof, ov andpaminophenol, pmethylaminophenol sulfate, p-hydroxyphenyl glycine, oandp-phenylenediamine, l-phenyl-3-pyrazolidone, alkali and alkaline earthmetal oxalates and formates and ferrous-ferric couple solutions.

Additionally, the image-forming materials or physical developers maycontain organic acids or alkali metal salts thereof, which can reactwith metal ions to form complex metal anions. Further, the developersmay contain other complexing agents and the like to improve imageformation and other properties found to be desirable in this art.

A preferred physical developer is that stabilized physical developercomprising silver ion, the ferrousferric couple reducing agent, acomplexing agent and an ionic surfactant as a stabilizing agent. Such adeveloper is described in U.S. Pat. No. 3,157,502 and PS and .6 B. Vol.I3, 1969, pp. 41-42, both incorporated by refernce.

The image-forming materials of this invention may be applied afterexposure of the copy medium to an image, or the image-forming materialscan, in the alternative, be incorporated along with the photoconductorin the copy medium prior to exposure. For example, both the reducingagent and oxidizing agent may be present in the copy medium as describedin U.S. Pat. No. 3,152,903, herein incorporated by reference. Or, in thealternative, only part of the image-forming materials may be present inthe copy medium at the time of exposure as, for example, when the copymedium is coated with silver nitrate prior to exposure and thensubsequent to exposure is developed by contacting with reducing agent.

The image-forming materials may be applied by any of the methods knownto the art as, for example, by dipping, coating, brushing, etc. Inaddition, the imageforrning materials may be applied in an electrolyticprocess such as described in U.S. Pat. No. 3,010,883.

Spectral sensitivity of the photosensitive copy me dium of thisinvention may be increased by means known to the art such as by dyesensitization, doping with foreign ions, exposure to ultravioletradiation, and the like.

The planographic master of this invention may be utilized to producepositive or negative prints of an original, depending upon how themaster is used. For example, the type of ink that is used on theplanographic master to produce the print may be varied. When a polarsolvent-based ink is utilized, such as a water or alcohol-based ink,such as disclosed in U.S. Pat. No. 3,209,683, incorporated herein byreference, then the ink adheres to the hydrophilic portions of themaster and a negative print is produced. However, when an oil base inkis utilized, the ink adheres to the oleophilic portions of the masterand a positive print of an original is produced. The preferred multiplecopy system of this invention utilizes an oil-based or greasy printingink.

Additionally, the planographic master produced by this invention can beutilized as a direct printing system or an offset printing system. Alsothe plate may be used in lithographic or driographic printing. See U.S.Pat. No. 3,51 1,178, incorporated by reference, for a definition ofdriography.

Binder agents are preferably used with the photosensitive materials tobind these materials to the carrier substrate. In general, these bindersare translucent or transparent so as not to interfere with transmissionof light to the photosensitive materials. Preferred binder materials arehydrophilic or hydrophobic organic materials such as polymers. Examplesof suitable polymers are synthetic polymers'such as butadienestyrenecopolymer, 'poly(alkyl acrylates) such as poly-(methyl methacrylate)polyamides, polyvinyl acetate, polyvinyl alcohol andpolyvinylpyrrolidone or natural polymers such as gelatin.

The exposure step of this invention is generally carried out by means ofactivating electromagnetic radiation. Thus actinic light, x-rays, orgamma rays are effective in exciting the photocatalyst. Beams ofelectrons and other like elemental particles may also be used in theplace of the ordinary forms of electromagnetic radiation for forming animage according to this invention.

These various activating means are designated by the term activatingradiation.

- lows:

- sodium sulfite 7 The inert substrate upon which the photoconductor ofthis invention is deposited comprises any suitable backing of sufficientstrength and durability to satisfactorily serve as a reproductioncarrier. The carrier substrate may be in any form such as, for example,sheets, ribbons rolls, etc. This sheet may be made of any suitablematerial such as'wood, metal, rag content paper, wood pulp paper,plastics such as, for example, polyethylene terephthalate .(Mylar), andcellulose-acetate, cloth, metallic foil and glass. Polyethylene coatedpaper having a gelatin subbing is an especially preferred support. Thetype of carrier substrate will depend upon the number of copies desiredfrom the planographic master produced. Generally, if a very high numberof copies is desired, it is desirable to have a more durable carriersheet.

The invention above described is exemplified as fol- EXAMPLE 1 Aphotosensitive copy medium comprising a paper support coated with afinely-divided titanium dioxide dispersed in a gelatin binder which hasbeen dyesensitized with Z-p-dimethylaminostyryl-4-methyl thiazolemethochloride is exposed to an image pattern from a tungsten lightsource for 1-2 seconds duration, thereby giving an exposureof 400 metercandle seconds.

The thus-exposed copy medium is then immersed in an aqueous solution of0.2 normal silver nitrate, then immersed in a Metol-sodium sulfite bath,and then contacted for a'few seconds with a pre-printing solution of thepotassium salt of 2-mercaptobenzothiazole. This processing is done bymachine at the rate of 4% inches per second. The processing rate isvaried from about 2-10 inches/sec with satisfactory results.

The thus prepared printing plate is now placed on an offset lithographicpress and used to print 500 copies which are positives of the. originalbecause the oil base ink adheres to the non-exposed portions of theplate.

The potassium salts of 5-mercapto-3-phenyl-1,3,4- t-hiadiazole-2-thione,2-mercaptobenzimidazole, 6- amino-2-mercaptobenzothiazole, the seleniumanalogue of Z-niercaptobenzothiazole are substituted for the potassiumsalt of 2-mercaptobenzothiazole in the above procedure to obtain'similarresults. EXAMPLE 2 A copy medium comprising a finely divided titaniumdioxide immersed in a high molecular weight polyvinylalcohol binder inthe absence of activating radiation is dipped in an aqueous solution ofsilver nitrate, dried, then contacted with an aqueous solution of thepotassium salt of Z-mercaptobenzimidazole and dried. This substrate isthen exposed to a source of ultraviolet light and then contacted with asolution of the following composition:

2 .0 Metol 2 0 2-lmidazole .1 N,N-dimethyl- O paraphenylenedidiaminesulfate Non-ionic surfactant 1.0 Water to 1 liter.

A printing plate is produced which is useful for making multiple copies.

EXAMPLE 3.

A polyethylene coated paper having a gelatinnitrocellulose subbing layeris coated with the following formulation:

TiO Slurry surfactant TiO, H,O

Coating Formulation TiO,-H,O Slurry (20% TiO,)

but

LANG

R Ekaline F (poly(ethylene oxide) nonionic surfactant) (10%)Photographic gelatin glycerin (50%) formaldehyde (3.7%)

w O06 0&0 we e em Bath 1 Bath 11 0.4 N AgNC),

20.0 g. Sodium Sulfite 20.0 g. Metolv 0.1 g. Z-imidazole 1.0 g.N-N-dimethyl-paraphenylenediamine sulfate 1.0 ml. Nonic 218 (non-ionicsurfactant) The potassium salt of 5,5 Diphenyl-Z-thiohydantoinDimethylformamide Bath Ill WWW The thus prepared printing plate is usedon an offset press with an oil base ink to print 500 copies which arepositives of the original. The metallic areas of the plate are thenon-printing areas.

A silver halide copy medium, exposed and processed as described aboveproduces a printing plate which is used for making copies on aconventional lithographic offset press using a greasy ink.

EXAMPLE 4 A polyethylene coated paper support having a gelatin subbinglayer is immersed in an aqueous solution of silver nitrate. This supportis then written on with a hydrophilic wax crayon which writing covers upportions of the support. The support is then contacted for a few secondswith a pre-printingsolution of the sodium salt of6-amino-2mercapto-benzothiazole, inked with a greasy printing ink andused on an offset press to produce copies which are negatives of crayonwriting.

In an alternative to writing with a wax crayon on the support which hasbeen contacted with silver nitrate is then written on by selectivelycontacting with a strong reducing agent for the silver nitrate asdisclosed in U.S. Pat. No. 3,108,932, incorporated herein by reference,which causes a silver image to form. This support is then contacted withthe above-mentioned pre-printing solution and the thus-prepared-printingplate is used to make multiple copies on an offset press.

EXAMPLE A porous anodized aluminum support is written on with a silvernitrate solutionand contacted with a preprinting solution of the sodiumsalt of mercaptobenzothiazole which forms a printing plate havingoleophilic areas useful for use on a press for making multiple copies.

What is claimed is:

l. A process of making a planographic printing plate comprising (1)exposing a copy medium comprising a photoconductor which after exposurecan be physically developed and contacting the copy medium withchemically reactive image-forming materials comprising a solution of asilver salt having reducible silver ions to form silver metal in theexposed areas and silver ions in the non-exposed areas, whichimage-forming materials remain chemically. reactive in the non-exposedareas of the copy medium but become substantially chemicallynon-reactive in the exposed areas, and (2) contacting the thus-treatedcopy medium with a compound having an oleophilic grouping and a groupingwhich enters into a chemical bond with the chemicallyreactive,image-forming materials of the non-exposed areas of the copy mediumthereby producing in these non-exposed silver ion containing areasoleophilic areas capable of being used as a printing plate and whereinthe compound having an oleophilic grouping and a grouping reactive witha chemically-reactive, image-forming material is'a polar solvent solublecompound of the general formula and (5); (7) an isothiocyanate group;and wherein R is at least one oleophilic group selected from alkylgroups, aryl groups, alkaryl groups, aralkyl groups, and a heterogrouping of the following general formula wherein R is selected from thegroup consisting of aryl, aralkyl, cycloalkyl and alkyl groups and whichR is linked to at least one of the two A atoms, and A is selected fromat least one of the atoms 0, N, S, and Se, and wherein the heterogrouping may be present either in an open arrangement or as a ringelement of a heterocyclic ring.

2. A process as in claim 1 wherein the compound 10 having an oleophilicgrouping and a grouping reactive with a chemically-reactive imageforming material is an alkali or alkaline earth metal salt of aheterocyclic mercaptan compound.

3. A process as in claim.2 wherein the mercaptan compound is at leastone of the group consisting of 5- mercapto-B-phenyll,3,4,-thiadiazole-2-thione, 2- mercaptobenzimidazole,6-amino-2-mercaptobenzothiazole, and Z-mercaptobenzothiazole.

4. A process as in claim 1 wherein the photoconductor comprises silverhalide or a metal containing photoconductor which becomes reversiblyactivated upon exposure to activating radiation.

5. A process as in claim 4 wherein the image-forming materialsadditionally comprise a reducing agent for said reducible silver ions.

6. A process as in claim.1 wherein the compound having an oleophilicgrouping is the alkali or alkaline earth metal salt of at least onecompound selected from the group consisting of l-phenyl-Z-thiourea,allylthiourea, l-acetyl-2-thiourea, Z-mercaptobenzoxazole,lphenyl-S-mercaptotetrazole, 2-mercapto thiazoline, l-dodecane thiol,4-6-diamino Z-mercaptopyrimidine',

phenyl isothiocyanate, thiourea, 2-mercapto-4-phenyl thiazole,Z-mercapto-benzothiozole, 6-amino-2- mercaptobenzo thiazole,Z-mercapto-benzimidazole, of 5-mercapto3-phenyl- 1 ,3,4-thiadiazole-2-thione, and 5,5 diphenyl-Z-thiohydantoine.

7. A process as in claim 6 wherein the compound having an oleophilicgrouping is the potassium or sodium salt of 5 ,5diphenyl-Z-thiohydantoine.

8. A process of making a planographic printing plate comprising (1)exposing a photosensitive copy medium comprising a photoconductor andcontacting the copy medium with chemically reactive image-formingmaterials comprising a solution of a silver salt having reducible silverions to form silver metal in the exposed areas and silver ions in thenon-exposed areas, which imageforming materials remain chemicallyreactive in the non-exposed areas of the copy medium but becomesubstantially chemically non-reactive in the exposed areas, and (2)contacting the thus-treated copy medium with a compound having anoleophilic grouping and a grouping which enters into a chemical bondwith said chemically-reactive, image-forming materials and whichcompound is the polar solvent soluble metal salt of the compound whichis at least one member selected from the group of dodecyl mercaptan;5-mercapto-3- phenyl-l 3 4-thiadiazole-2-thione; 2-mercaptobenzimidazole; 6-amino-2-mercaptobenzothiazole;2-mercaptobenzothiazole; and 5 ,5 diphenyl-Z- thiohydantoin.

9. A process as in claim 8 wherein said copy medium photoconductorcomprises silver halide, titanium dioxide or zinc oxide.

10. A process as in claim 9 wherein the imageforming materials comprisea reducing agent for said reducible silver ions.

2. A process as in claim 1 wherein the compound having an oleophilicgrouping and a grouping reactive with a chemically-reactive imageforming material is an alkali or alkaline earth metal salt of aheterocyclic mercaptan compound.
 3. A process as in claim 2 wherein themercaptan compound is at least one of the group consisting of5-mercapto-3-phenyl-1,3,4,-thiadiazole-2-thione,2-mercaptobenzimidazole, 6-amino-2-mercaptobenzothiazole, and2-mercaptobenzothiazole.
 4. A process as in claim 1 wherein thephotoconductor comprises silver halide or a metal containingphotoconductor which becomes reversibly activated upon exposure toactivating radiation.
 5. A process as in claim 4 wherein theimage-forming materials additionally comprise a reducing agent for saidreducible silver ions.
 6. A process as in claim 1 wherein the compoundhaving an oleophilic grouping is the alkali or alkaline earth metal saltof at least one compound selected from the group consisting of1-phenyl-2-thiourea, allylthiourea, 1-acetyl-2-thiourea,2-mercaptobenzoxazole, 1-phenyl-5-mercaptotetrazole, 2-mercaptothiazoline, 1-dodecane thiol, 4-6-diamino 2-mercaptopyrimidine, phenylisothiocyanate, thiourea, 2-mercapto-4-phenyl thiazole,2-mercapto-benzothiozole, 6-amino-2-mercaptobenzo thiazole,2-mercapto-benzimidazole, of5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione, and 5,5diphenyl-2-thiohydantoine.
 7. A process as in claim 6 wherein thecompound having an oleophilic grouping is the potassium or sodium saltof 5,5 diphenyl-2-thiohydantoine.
 8. A process of making a planographicprinting plate comprising (1) exposing a photosensitive copy mediumcomprising a photoconductor and contacting the copy medium withchemically reactive image-forming materials comprising a solution of asilver salt having reducible silver ions to form silver metal in theexposed areas and silver ions in the non-exposed areas, whichimage-forming materials remain chemically reactive in the non-exposedareas of the copy medium but become substantially chemicallynon-reactive in the exposed areas, and (2) contacting the thus-treatedcopy medium with a compound having an oleophilic grouping and a groupingwhich enters into a chemical bond with said chemically-reactive,image-forming materials and which compound is the polar solvent solublemetal salt of the compound which is at least one member selected fromthe group of dodecyl mercaptan; 5-mercapto-3-phenyl-1, 3,4-thiadiazole-2-thione; 2-mercaptobenzimidazole;6-amino-2-mercaptobenzothiazole; 2-mercaptobenzothiazole; and 5,5diphenyl-2-thiohydantoin.
 9. A process as in claim 8 wherein said copymedium photoconductor comprises silver halidE, titanium dioxide or zincoxide.
 10. A process as in claim 9 wherein the image-forming materialscomprise a reducing agent for said reducible silver ions.